Crystallizer for the continuous casting of a metal product, and corresponding casting method

Abstract

Crystallizer for the continuous high-speed casting of a metal product (P), which has a casting cavity (13) defined by walls (14) connected to each other in correspondence with edges (15) and provided with cooling means (16).

Description

FIELD OF THE INVENTION[0001]The present invention concerns a crystallizer for the continuous casting at high speed of metal products, such as billets or suchlike.[0002]In particular, the crystallizer according to the present invention allows to cast billets with a much higher casting speed than known crystallizers, increasing productivity, maintaining a high quality of the product and without requiring containing devices downstream of the crystallizer.[0003]The crystallizer according to the present invention is particularly suitable for casting and rolling processes using the endless mode, that is, without interruptions between casting and rolling.[0004]It is understood that the crystallizer as above can also be used for other casting and rolling modes, such as billet-to-billet or semi-endless for example.BACKGROUND OF THE INVENTION[0005]It is known that in continuous casting plants the heart of the casting machine consists of the crystallizer into which the liquid metal is introduc...

AI Technical Summary

Benefits of technology

[0056]The Applicant has tested that by casting a product with an octagonal-shaped section it is possible to reach higher casting speeds than in known solutions, for example from 6 m / min up to 15 m / min, and at the same time it is possible to increase the self-supporting capacity of the solid structure of the product even for rather thin skin thicknesses.

[0076]In light of the above, it is therefore possible to keep the high quality characteristics of the cast product and to keep the casting speed high from 6 m / min up to 15 m / min, thus obtaining a high productivity of the plant comprised between approximately 50 ton / h and about 150 ton / h.

Problems solved by technology

The swelling or bulging can lead to the formation of cracks which, if they extend up to the external surface, cause the skin to break, with consequent leakage of liquid metal (breakout) and consequent interruption in the production, dirtying and damage to the plant, and potential danger for the workers.

In fact, if for some reason the contact between the skin and the containing sectors were to take place not in the best possible way, then there are concrete possibilities that the skin may be pinched or torn, thus incurring potential breakouts.

The alignment operations are complex and are carried out manually off-line by specialized operators, requiring several hours of work and consequently affecting the operating maintenance costs.

Furthermore, the maintenance of the containing sectors requires adequate spare parts in the warehouse, with related management costs, and imposes constraints on the operation of the casting machine if multiple breakouts occur which are close to each other in time.

Square section billets also have a non-uniformity in the surface temperature between the center-face of the flat walls and the edges; this non-uniformity is present both inside and outside the crystallizer, causing defects during the casting step and / or in the subsequent rolling processes downstream, as explained below.

As one gets closer to the edges, there is therefore a worsening of the contact, and therefore a decline in the ability to remove heat, and the liquid metal consequently has difficulty in solidifying.

This results in localized thinning of the skin near the edges.

These cracks, also called “off-corner cracks”, lead to a decline in the quality of the billet and can lead to deformations of the cast section, for example accentuating the rhomboid shape, and in extreme cases they can reach the external surface, causing the skin to break and resulting spillage of liquid metal.

The rhomboid shape effect also has repercussions downstream from the casting, for example, in the rolling stands, causing jamming.

Furthermore, the frequency of these problems increases as the casting speed increases, which imposes a limit on the maximum achievable speeds and therefore on the productivity of the casting machine.

Following the secondary cooling, the edges are colder than the center-face since they receive cooling simultaneously on the two sides of the edge and this can cause the onset of defects and / or cracks in the zone of the edges in the subsequent rolling step.

All the problems described above with reference to square section tubular crystallizers have, until now, significantly limited the casting speeds obtainable.

On the other hand, however, round products do not allow to reach high casting speeds since the internal taper of the crystallizer, although studied and optimized, does not allow in all process conditions a perfect and constant contact with the cast product, and therefore, during shrinkage, the solidified skin tends to detach itself from the walls of the crystallizer, reducing the uniformity of the heat exchange.

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